Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $89.58   6.855%   $95.7207   $95.72   $95.70   $95.70  
  Purchase #2 $229.59   9.363%   $251.0865   $251.09   $251.10   $251.10  
  Purchase #3 $125.46   6.497%   $133.6111   $133.61   $133.60   $133.60  
  Purchase #4 $168.57   6.122%   $178.8899   $178.89   $178.90   $178.90  
  Purchase #5 $23.48   13.191%   $26.5772   $26.58   $26.60   $26.60  
  Purchase #6 $159.90   12.650%   $180.1274   $180.13   $180.15   $180.10  
  Purchase #7 $244.45   4.320%   $255.0102   $255.01   $255.00   $255.00  
  7 purchase totals = $1,041.03       $1,121.0230   $1,121.03   $1,121.05   $1,121.00